Unborn Foal Identified from Ancient Horse Fossil

Eurohippus messelensis – Fossil Reveals Ancient Foetus

The fossilised remains of an ancient, prehistoric horse that once roamed southern Germany has revealed the presence of an unborn foal.  Scanning electron microscopy of the beautifully preserved fossil has revealed the bones of a foetus, this is the oldest fossilised equine foetus discovered to date and reveals that the horse reproductive system was already highly developed by the early Middle Eocene.

Ancient Horse Fossil Reveals Unborn Foal

Eurohippus foetus fossil from the Messel Shale.

Eurohippus foetus fossil from the Messel Shale.

Picture Credit: Senckenberg Research Institute

The position of the foetus in the mare is marked by the white ellipse in the picture above.  Scale bar equals 10 centimetres.  The fossil has been set in resin, this is a standard procedure to help preserve the fossils from the Messel oil shales.

Details of the research, conducted by scientists from the Senckenberg Research Institute (Frankfurt) and the University of Veterinary Medicine (Vienna), have been published in the academic journal PloS One.  The fossil, an early horse called Eurohippus messelensis, was excavated from the Messel Shales near Darmstadt (Germany) in 2000 but it was only after recent high resolution micro-X-ray studies in combination with the scanning electron microscopy that the 12.5 centimetre long foetus was found.  Most the skeleton is intact (post cranial material) and elements of the placenta can be determined.  Based on a comparison with modern horses, the position of the foetus, which was near full term at the time of death, is almost identical to that seen in today’s mares which are at roughly the same stage of pregnancy.  The death of the potential mother-to-be and the unborn foal are not related to any potential complications that arose during parturition.  It seems that this little, ancestral horse that was just thirty centimetres high at the shoulder, ended up in a large, deep lake and was quickly buried in the oxygen depleted sediments at the bottom.  These sediments eventually became the oil shales which make this part of southern Germany so famous.

A Line Drawing of the Exposed Side of the Foetus

Scale bar 10 cm (A and B)

Scale bar 10 cm (A and B)

Picture Credit: Senckenberg Research Institute, Jörg Habersetzer; line drawing (b) by  Jens Lorenz Franzen.

The picture above (a) shows the foetus position in relation to the bones of the adult and maps out the position of the placenta (line drawing b).

How did the Ancient Horse Die?

The oil shales of Messel contain a huge amount of fossils, both aquatic and terrestrial species, but how did this rich fossil assemblage come about?  This part of Germany was located ten degrees further south during the early Middle Eocene than it is today.  It is believed to have been a very geologically active area and infrequent releases of large concentrations of poisonous gases from the deep lakes in the area could have devastated the local ecosystem.  Deadly releases of carbon dioxide mixed with hydrogen sulphide would have quickly suffocated animals in the water and once these gases had reached land they would quickly overcome any animal in close proximity to the shore.  Corpses would have been washed into the lake by rains and eventually they would have drifted down to the bottom, where the lack of oxygen and bacteria would have facilitated their excellent preservation.  This theory also accounts for the number of bird and bat fossils found in these oil shale deposits.  Any animal flying over the lake and encountering the gas cloud would be affected and fall into the water.  Bat fossils are amongst the most numerous of all the terrestrial vertebrate fossils found at the Messel quarry site.

Such a scenario was depicted in the “Walking with Beasts” episode “New Dawn” made by the BBC.

Eurohippus (E. messelensis) is one of a number of early ungulates known from the Messel shales of Germany.

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